Aesthetix Calypso getting hot on the left side

I've just bought a used Aesthetix Calypso preamp and I'm very happy with its sound.
But I'm worried as it gets hot over the left side of it.
The source of the heat is on the left side of the common board, just on the left of the AC cable channel before it enter the transformers enclosure.
It's definitely hotter than on the right side, but not so hot that I couldn't place my hand on the cover over it.

Do you think this is normal?